Problem: $ F = \left[\begin{array}{rrr}0 & 2 & 1 \\ 2 & 0 & 2 \\ 0 & 0 & 1\end{array}\right]$ What is $ F^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}0 & \frac{1}{2} & -1 \\ \frac{1}{2} & 0 & -\frac{1}{2} \\ 0 & 0 & 1\end{array}\right]$